Benzoyl peroxide and its derivatives form a family of useful initiators used widely in the polyester and plastics industry. For example, such peroxides catalyze the polymerization of styrene, vinyl chloride, and the like, and the cross-linking of unsaturated polyester compositions. Dry peroxides of this family are shock sensitive and flammable. It is possible to add inert plasticizers to reduce the danger in handling, and, commercial pastes containing 50 or 55% of the peroxide in tricresyl phosphate or in phthalate esters are now widely available; these can contain up to 15% by water, too, to substantially further reduce safety hazards.
In U.S. Pat. No. Re. 28,818, it is proposed to further stabilize such compositions against separation in storage by adding a small, effective amount of an expensive hydrophobic alkyl-group-containing silicone. In U.S. Pat. No. 3,731,791, creamy catalyst pastes are described comprising benzoyl peroxide, dimethyl phthalate, ground calcite and di-2-ethylhexyl phthalate. A stable paste with a unique whipped cream-like consistency is disclosed in applicant's earlier filed copending U.S. patent application Ser. No. 7,581, filed Jan. 29, 1979 now U.S. Pat. No. 4,255,277. This comprises a paste of granular peroxide, water, a non-reactive plasticizer, such as dibutyl phthalate and some mineral filler. A stable, reactive paste is disclosed in commonly assigned Charles Donald Dudgeon and John J. Keane's copending and concurrently filed U.S. patent application Ser. No. 135,787, filed of even date herewith. Such catalysts comprise a diacyl peroxide, a vinyl reactive fumarate, e.g., diethyl fumarate or dibutyl fumarate, some mineral filler and, optionally, water. The reactive fumarate provides for curing into polyester resins and elevates their heat distortion temperature in a most desirable way. The foregoing patents and applications are all incorporated herein by reference.
While the pastes of the prior art can now be produced in a stable, non-separating, pumpable, mixable form with the ability to produce cured resins without substantial unreacted plasticizer content, long term aging can stand improvement, especially under accelerated, above room temperature conditions.
A technique has now been found to overcome such problems, and this is by providing a peroxide paste with a vinyl reactive monomeric fumarate diester of a very specific type, namely, a di(hydroxyloweralkoxyloweralkyl) fumarate. Such a composition is more stable on accelerated aging than any heretofore known, and provides high heat deflection temperatures in the ultimate product, e.g., a mine bolt resin or a rapid-cure accelerated polyester.